The invention relates to an additive for improving the flow properties of paraffin-containing mineral oils and mineral oil distillates, containing flow improvers based on ethylene-vinyl ester copolymers and terpolymers, polar nitrogen compounds and ethers and/or esters as solubilizers.
Crude oils and middle distillates obtained by distillation of crude oils, such as gas oil, diesel oil or heating oil, contain, depending on the origin of the crude oils, various amounts of n-paraffins, which, when the temperature is reduced, crystallize out as platelet-shaped crystals and in some cases agglomerate with inclusion of oil. This crystallization and agglomeration causes an impairment of the flow properties of the oils or distillates, which can result in problems during the recovery, transport, storage and/or use of the mineral oils and mineral oil distillates. During transport of mineral oils through pipelines, the crystallization phenomenon can cause deposits on the walls of the pipes, especially in winter, and in individual cases, for example during stoppage in a pipeline, can even cause complete blocking thereof. During storage and further processing of the mineral oils, it may furthermore be necessary in winter to store the mineral oils in heated tanks. In the case of mineral oil distillates, the crystallization may result in blockage of the filters in diesel engines and furnaces, preventing reliable metering of the fuels and in some cases causing complete interruption of the supply of the fuel or heating medium.
In addition to the classical methods of eliminating the crystallized paraffins (thermal, mechanical or using solvents), which merely involve removal of the precipitates which have already formed, recent years have seen the development of chemical additives (so-called flow improvers), which, by interacting physically with the precipitating paraffin crystals, result in their shape, size and adhesion properties being modified. The additives act as additional crystal nuclei and in some cases crystallize with the paraffins, resulting in an increased number of relatively small paraffin crystals having a modified crystal shape. The modified paraffin crystals have a lower tendency toward agglomeration, so that the oils to which these additives have been added can still be pumped and/or processed at temperatures which are frequently more than 20.degree. lower than in the case of oils containing no additives.
Typical flow improvers for crude oils and middle distillates are copolymers and terpolymers of ethylene with carboxylates of vinyl alcohol.
A further object of flow improver additives is dispersion of the precipitated paraffin crystals, i.e. inhibition or prevention of sedimentation of the paraffin crystals and thus of the formation of a paraffin-rich layer at the base of storage tanks.
The prior art discloses, inter alia, polar nitrogen compounds as paraffin dispersants. These can generally be used together with copolymers or terpolymers of ethylene and vinyl esters as additives to mineral oils and mineral oil distillates.
However, the use, in many cases desired, of concentrates of polar nitrogen compounds as paraffin dispersants together with copolymers and terpolymers of ethylene and vinyl esters encounters technical difficulties, since these substances have only very poor solubility in one another. The prior art therefore proposes various solubilizers, but their action is frequently unsatisfactory.
DE-A-40 19 623 discloses crystallization inhibitors for paraffins in petroleum fractions comprising fatty amines and solutions of benzoic and formic acids in methanol, ethanol, cyclohexanol or isopropanol.
EP-A-0 104 015 discloses the use of weak organic acids, in particular aromatic acids, such as benzoic acids, alkylphenols and alkarylsulfonin acids, for improving the solubility of nitrogen compounds in oils.
U.S. Pat. No. 4,210,424 discloses the use of polymers derived from carboxylic esters and carrying alkyl side chains having 6 to 30 carbon atoms, and/or from C.sub.8 -C.sub.18 -alkanols as solubilizers in compositions comprising ethylene copolymers, paraffin waxes and nitrogen compounds.
EP-A-0 733 694 discloses solvent mixtures of aliphatic or alicyclic alcohols having at least 4 carbon atoms and aromatic hydrocarbons in a ratio of from 10:1 to 1:2. The solvents are used to form a homogeneous mixture together with oil-soluble additives containing NR groups, where R is a hydrocarbon radical having 8 to 40 carbon atoms.
The object was therefore to find more efficient solubilizers between the polar nitrogen compounds and the ethylene/vinyl ester copolymers and terpolymers.
Surprisingly, it has been found that ethers and esters and mixtures thereof are excellent solubilizers for these flow improver combinations.